Two stars M1 and M2 of equal mass make up a binary star system.
They move in a circular orbit that has its center at the midpoint
of the line that separates them. If M1 = M2 = 7.20 sm (solar mass),
and the orbital period of each star is 8.45 days, find their
orbital speed. (The mass of the sun is 1.99 1030 kg.)